Mercury contact device



June 21, 1949. g E, PQLLARD, JR 2,473,693

, uancumr CONTACT nnvxcn Filed Sept. 19, 1947 2 Sheds-Sheet 1 RESTORING FORCE l l l I l l DIS TIA/CE INVEN TOR C. E. POLLARD BY I A T TORNEY une 21', 1949.

cs5. POLLARD, JR uncua CONTACT DEVICE Filed Sept. 19. 1947 2 Sheets-Sheet. 2

Patented June 21, 1949 MERCURY CONTACT DEVICE Charles E. Pollard, Jr'., Hohokus, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application September 19, 1947, Serial No. 775,081

6 Claims. 1

This invention relates to circuit makers and breakers and particularly to relay type apparatus having wetted mercury contacts.

The object of the invention is to provide a very sensitive and fast acting relay having wetted mercury contacts.

In accordance with this invention the element constituting the armature of the relay is in the form of a small thin sheet of magnetic material suspended by mercury and having no mechanical connection with any other part of the device except to make contact with an electrode when it is energized.

The relay is in the form of a sealed envelope having a pool of mercury at the bottom. Rising from this pool is a mercury wick in the form of a pair of parallel mercury wetted wires spaced sufficiently close together, so that mercury will rise by capillary action to the tops thereof. These wires terminate in two flat parallel plates somewhat smaller than the armature which is suspended between them and. held in position by the force of surface tension of the mercury. Placed above or to one or both sides of this armature plate is or are electrodes with which the armature makes contact when through magnetic force it is caused to slide through the mercury in the plane of its own surface. By this means the mass of the armature may be extremely small so that it must depend on the surface tension of the supporting mercury in addition to its own weight for its restoring force. Due to the extremely small size of the moving magnetic piece, its weight forms only a minor fraction of the restoring force which is effective. The mass being very small the movement is very fast and the sensitivity is great. The armature being in the form of a thin flat plate which moves in the plane of its own surface the frictional retardation of the mercury is small and since there is movement of only a trifling amount of mercury the mass of such displaced mercury is not added to the mass of the armature.

The surface tension force exerted by the mercury depends upon the angle with which the meniscus makes contact with the metal surface and hence acts'like a spring whose increase in tension is non-linear with displacement. Therefore, when the armature plate is in its normal position the equivalent spring force will be zero since it is balanced on all four edges thereof. When the plate is moved upwardly by magnetic force, however, the equivalent spring force rises in a characteristic exponential form so that after the meniscus has been drawn out to a point where its upper edge is practically parallel with the plane of the plate, no further force is exerted. For this reason the relay becomes far more sensitive than one in which the armature is restrained by the conventional spring operation under the conventional linear characteristic.

Again, and for this same reason, the two plates used for terminating the mercurywick wires are made of very thin material with sharp edges and of somewhat greater'area than the area of the supporting plate. The function of this plate is to prevent the meniscus of mercury from spreading out over a horizontally wetted surface to the point where its capillary attraction to such surface becomes zero. By this means the tension provided by the mercury on each side of the armature plate is maintained at the same value whereby the armature plate is held firmly between the plates and at an equal distance from each.

Due to this type of construction the relay is spoken of familiarly as the sandwich relay, the filling of the sandwich being the armature piece.

A feature of the invention may, therefore, be stated as the combination of three very thin magnetic and mercury wettable plates sandwiched with a filling of mercury whereby the mercury trapped therebetween is prevented from escaping.

Another feature of the invention may be stated as a means for securing an armature and exerting thereon a restraining or restoring force having non-linear characteristics whereby the movement of the armature becomes unimpeded after the restraining force has been overcome in the first slight movement thereof.

Other features will appear hereinafter.

The drawings consist of two sheets having eleven figures as follows:

Figs. 1 and 2 are very greatly enlarged fragmentary views of the contact arrangement in which Fig. 1 shows the armature in its normal unoperated position and Fig. 2 shows the armature is its operated position;

auaooa Fig. 3 is a graph to illustrate the fact that the restoring force on the armature is non-linear;

Fig. 4 and Fig. 5 show sectional views of the contact arrangement, Fig. 4 looking at the face of the armature arrangement and Fig. 5 looking at the side thereof;

Fig. 6 is a similar sectional view of a contact arrangement in which the armature works against two contact pieces;

Figs. 7 and 8 show a similar arrangement in which an armature will move sidewise in either direction to make contact with on or another contact. In Fig. 7 an arrangement of a neutral polarized relay is shown in which the armature makes contact normally with neither of its contacts but may be moved in either direction at will. Fig. 8 is a side view of the same;

Fig. 9 is an enlarged fragmentary view showing how a relay with its armature normally resting against the back contact may be caused to act as a conventional transfer to make connection with a front contact;

Fig. 10 is an alternative arrangement in which the armature instead of being square as shown in the other figures is oblong for purposes which will be hereinafter described; and

Fig. 11 is a perspective showing of a scaled contact device in a solenoid.

The contact device consists essentially of a glass envelope i in which a pair of magnetic material wires 2 and 3 is sealed at the bottom and extends upwardly through a pool of mercury 4. The wires 2 and 3 are spaced sufficiently close together to form a capillary path for the mercury which thereupon rises to the armature arrangement. This consists of a pair of plates 5 and 6 attached as by welding to the upper portions of the wires 2 and 3. A thin plate of magnetic material I and 8 is then fixed to each of these plates. All of this material is easily wetted by mercury and, therefore, the space between the plates 1 and 8 will be filled with mercury. A very small and thin plate 9 is held mid-way between the two plates I and 8 by the surface tension of the mercury provided by its meniscus at the edges of these various plates. Thus the force of the surface tension will hold the armature plate 9 firmly in the position shown in Figs. 1 and 4.

Spaced a short distance above the upper edge of the plate 9 will be a tube Ill having fixed thereon a contact piece ii at right angles to the plane of the armature piece 9. When the solenoid in which the unit shown in Figs. 4 and 5 is inserted is energized then the armature piece 9 will move upwardly and make contact with the contact piece ll as illustrated in Fig. 2. This contact piece H is also wetted by mercury so that the contact will be substantially as shown in Fig. 2.

It should be noted that the armature piece 9 is of very small dimensions being a square sheet of magnetic material about A; by ,2; inch square and .003 inch in thickness and weighing less than 5 milligrams. Due to this very small weight the restoring force of the armature practically resides in the surface tension of the mercury, the weight being only a minor fraction of this restoring force.

It should also be noted that the restoring force depends upon the angle with which the meniscus of mercury meets the surface of the armature piece 9. This is illustrated in Fig. 3. As the armature moves, the meniscus of mercury becomes more nearly parallel to the surface of the plate so that the restoring force soon reaches a maximum point beyond which it does not increase regardless of the distance over which the armature moves. This contrasts greatly with the use of a restoring spring which is normally directly proportional to the extent of the movement thereof.

The thin plates 1 and 8 are provided to control the surface tension of the mercury in order to hold the armature element firmly mid-way therebetween.

With this 'construction the movement of the armature is extremely fast and the relay is very sensitive.

In Fig. 6 a similar arrangement is shown except that there are two contacts i2 and I3 affixed to the two magnetic material wires I4 and I 5 sealed through the glass tube I.

In Figs. 7 and 8 a contact device is shown in which the armature piece 9 may be caused to move either to the left to make contact with a contact piece It or to the right to make contact with a contact piece ll. The contact pieces I6 and I! are affixed respectively to the wires l8 and I9 sealed through the top of the glass envelope 20.

It is not necessary that both of the wires 2 and 3 be sealed through the bottom of the envelope I. One of them may be terminated in the seal or as an alternative arrangement no electrical connection may be made to either of these wires but an arrangement in which the circuit is closed from a wire It to a wire I 5 through the armature piece 9 may be used.

Fig. 9 is a fragmentary view of an arrangement in which the armature piece 9 normally rests against a contact 2! but may be moved therefrom to the contact 22 to provide a conventional transfer arrangement.

Fig. 10 is an enlarged fragmentary view in which the plate 23, the plate 24 and the armature piece 25 are made oblong so as to prevent skewing of the armature in its movement.

In Fig. 11 a sealed contact device of the nature above described numbered 26 is shown inserted in a solenoid 29 so that when this solenoid is energized a circuit between the electrodes 21 and 28 will be completed.

It will be understood that many other alternative arrangements based upon this fundamental principle may be provided.

What is claimed is:

1. In a circuit maker and breaker, a sealed envelope having a pool. of mercury therein, a mercury wick sealed in said envelope and extending from said pool of mercury, a pair of parallel plates terminating the upper end of said wick and spaced sufficiently near each other to maintain mercury therebetween, a magnetically movable armature in the form of a thin plate of magnetic material conforming in shape but of slightly larger area than said plates suspended between said plates and supported by the force of the surface tension of said mercury and an electrode in cooperative relationship with said armature normally out of contact with said armature but within the plane of the surface of said armature.

2. In a circuit maker and breaker, a sealed envelope having a pool of mercury therein, a mercury wick extending through said pool of mercury, a pair of parallel plates terminating the upper end of said wick and spaced sufficiently near each other to maintain mercury therebetween, a magnetically movable armature in the form of a thin plate of magnetic material conforming in shape but of slightly larger area than said plates suspended between said plates and supported by the force of the surface tension of said mercury and an electrode in cooperative relationship with said armature normally out of contact with said armature but within the plane of the surface of said armature.

3.In a circuit maker and breaker, a sealed envelope havin a pool of mercury therein, a mercury wick extending through said pool of mercury, a pair of parallel plates terminating the upper end of said wick and spaced suiilciently near each other to maintain mercury therebetween, a magnetically movable armature in the form of a thin plate of magnetic material conforming in shape but of slightly larger area than said plates suspended between said plates and supported by the force of the surface tension of said mercury and an electrode. in cooperative relationship with said armature normally out or contact with said armature but within the plane of the surface of said armature and a support of magnetic material for said electrode sealed in the said envelope.

'4. In a circuit maker and breaker, a sealed envelope having a pool of .mercury therein, a mercury wick secured to an electrode sealed through said envelope at the bottom end thereof and extending through said pool of mercury, a pair of parallel plates terminating the upper end of said wick and spaced sufilciently near each other to maintain mercury therebetween, a magnetically movable armature in the form of a thin plate of mercury wetted magnetic material conforming in shape to but of slightly larger area than said plates suspended between the said plates and supported by the force of the surface tension of said mercury and a mercury wetted contact in cooperative relationship with. said armature above but normally out of contact with said armature having a substantially linear contact surface normal to the plane of said arma-- ture.

5. In a mercury contact relay, an armature in the shape of a rectangular thin plate of mercury wetted magnetic material, of the order of .016 square inch in area, .003 inch in thickness and less than 5 milligrams in weight, sandwiched be-' tween two similar plates slightly less in area and conforming in shape to said armature and supported by the surface tension of mercury filling the spaces between said armature and said plates.

6. In a mercury contact relay, an armature weighing less than 5 milligrams sandwiched between two mercury wetted surfaces, each of said surfaces comprising a plane face of a thin plate of magnetic material smaller than the said armature but conforming thereto in shape, the edges of said plates being insuflicient in breadth to allow the meniscus of mercury held between said plate and said armature to approach parallelism with the plane of said edge, whereby said armature is supported by the surface tension of the said mercury.

CHARLES E. POLLARD, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,295,602 Pollard Sept. 15, 1942 2,317,695 Pollard Apr. 27, 1943 

